Cu2OTiO2heterostructure nanotube arrays prepared by an.docx

Cu2OTiO2heterostructure nanotube arrays prepared by an.docx

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Cu2OTiO2heterostructurenanotubearrayspreparedbyan

Cu2O/TiO2heterostructurenanotubearrayspreparedbyanelectrodepositionmethodexhibitingphotocatalyticactivityforCO2reductiontomethanol

JunyiWanga,GuangbinJia,*,YousongLiua,M.A.Gondalb,XiaofengChanga

a.CollegeofMaterialsScienceandTechnology,NanjingUniversityofAeronauticsandAstronautics,Nanjing211100,China;

b.PhysicsDepartment,KingFahdUniversityofPetroleum&Minerals,Dhahran31261,SaudiArabia.

*Thecorrespondingauthor:

Prof.Dr.GuangbinJi

Tel:

+86-25-52112902;Fax:

+86-25-52112900

E-mailaddress:

gbji@

PreparationofCu2O/TNTs

TheCu2O/TNTscompositeswereobtainedbyCu2Oelectrochemicaldepositioninaconventionalthree-electrodecell,usingtheTNTs,Ag/AgClandPtastheworking,reference,andcounterelectrodes,respectively.Theelectrolytewaspreparedbydissolving0.4MCuSO4in3molL−1lacticacidsolution,andwasadjustedtopH=11.0withNaOHsolutionwiththeexistenceoflacticacidwhichcanstabilizethecopperionsinalkalinesolutiontoformcopperlactatecomplex[1-2].Theelectrochemicaldepositionwascarriedoutatapotentialof-0.8VreferencedtoAg/AgCl.Theelectrolytewaskeptataconstanttemperatureof25◦C,magneticallystirredduringthedepositionprocess.Threetypesofsampleswereobtainedbyvaryingtheconcentrationofelectrodepositioncharges:

0.5C,1.0Cand1.5C.Aftertheelectrodepositionprocess,thesampleswerewashedwithdeionizedwater,placedinavacuumandannealedinatubularfurnaceat200◦Cfor10mininN2atmosphere.

DetailsaboutPhotoelectrochemicalmeasurements

ThephotoelectrochemicalmeasurementswerecarriedoutwithCHI660Dinathree-electrodecellin0.05MNa2SO4electrolytesolutionwithCu2O/TNTssaturationmercuryelectrodewereusedastheworkingelectrode,counterelectrodeandreferenceelectrode,respectively.A500WXenonlampwithalightintensityof400mW/cm2wasusedasthelightsource.Thewavelengthsoftheincidentlightweregreaterthan400nmusinga400nmcut-offfilter.

DetailsaboutphotocatalyticreductionofCO2

ThelaserusedasthelightsourceofexcitationinthisstudywasthethirdharmonicofthepulsedNd:

YAGlaser（ModelSpectraPhysicsGCR250–10）laser.Thephoto-catalyticreactorisacylindricalstainlesssteelcellwithquartzwindowsonthetoptoenablethetransmissionofbothUVandVisiblelightradiation.Atthebottomofthecell,thereisagasinletwithaneedlevalvethatletstheCO2gaspassthroughthedistilledwaterandalmostatthesamelevel,inordertodispensethesamplethroughthesyringethereisanoutletfixedwiththerubberseptumattheoppositeside.Thewholecelliskeptonamagneticstirrerthatconstantlyreplenishesthephoto-catalystinthepathoflaserradiations.Attentionwaspaidtohaveabetterinteractionofincidentradiationswiththephotocatalystandkeepthewaterlevelabovethecatalysttobeminimum（almosttothelevelofthecatalystplatform）.Sincethequantityofthesampletakenforgaschromatographicanalysisateachtimewasaround4.0μl,thewaterleveldidnotdecreaseduetothesamplewithdrawalfromthereactioncell.Thereactioncellwascleanedanddried,and3cm×3cmcatalystwasloadedalongwith100mldistilledwaterandthentightlyclosedandcheckedforleaksupto50psipressure.HighpurityCO2gas（99.99%）wasintroducedthroughreactorinletsandthereactorpressurewasmaintainedat50psi.Priortoturningonthepulsedlaser,CO2gaswaspurgedinto100mlwatercontaining3cm×3cmcatalystfor30mintosaturatetheaqueoussolutionofthereactorwithCO2.Afterapredeterminedirradiationtime,theliquidsampleswerewithdrawnfromthereactorusingsyringewithoutopeningthereactorandweresubjectedtoGCanalysis.

Theliquidsampleswereanalyzedfortheendproductslikemethanolandotherhydrocarbonsusingagaschromatographequippedwithflameionizationdetector0FID）.TheseparationofthecomponentswascarriedoutonRtx-Waxcolumn（dimensions:

30mx0.32mmx0.32mm）obtainedfromRestekusingtemperature-programmedconditions.Fortheanalysis,4.0μlproductsamplewasinjectedintothegaschromatographandtheoperatingconditionswereasfollows:

Oventemperaturewassetat40oC,increasedto90oCatheatingrateof5oC/minandthenincreasedto180oCattherateof50oC/mintoeluteallthecomponentsbeforeinjectinganothersample.Theinjectoranddetectorswerebothsetat200oCandheliumwasusedasacarriergas.Thetotalanalysisruntimewas11.8min.Acalibrationplotwasdevelopedusingastandardmethanolsolutionindistilledwaterforcalculatingtheamountofmethanolproducedasafunctionofirradiationtime.

Analysisandquantificationofmethanolproduct

Gaschromatography（GC）techniquewasemployedtoverifyandquantifythemethanolasanendproductfromtheCO2reductionoverCu2O/TNTsnanocomposite.ItisdepictedinFig.S-1（a）thattheretentiontimeofstandardmethanolis2.46minsfortheGCselectedparametersandtheusedcolumn.TherelationshipbetweenGCpeakareaandmethanolconcentrationwasconfirmedbyusingstandardconcentrationsofmethanolforcalibrationasmentionedearlieranddepictedinFig.S-1（b）,whichexhibitsclearlyalineartrend.

Fig.S-1（a）.GCpeakpositionsusingstandardmethanol;（b）.CalibrationcurveofmethanolconcentrationvsGCpeakarea.

DetailsaboutphotocatalyticdegradationofTNTsandCu2O/TNTs

Photodegradationexperimentswerecarriedoutina100mLconicalflaskcontaining50mL,dyeAcidorange（AO）solutionwithinitialconcentrationof1ppmunderstirringconditions.ThepreparedCu2O/TNTscompositeswerekeptinaquartzdeviceandthereactionsystemwasilluminatedundervisiblelightafterthesamplesreachedadsorptionequilibriumsaccordingtopreviousreport[3].4mLofthesuspensionwaswithdrawnthroughouttheexperimentafterevery20min.ThesampleswereanalyzedbyaUV-Visspectrophotometer（SHIMADZUUV-3600）.

PhotocatalyticactivityforthedegradationofAO

InordertofurtherprovetheconstructionofCu2O/TNTsheterojunction,thephotocatalyticactivityoftheTNTsandCu2O/TNTssampleswereevaluatedbythedegradationofAOdyemoleculesinwaterunderilluminationwitha300WXearclamphavinganoutputintensityof400mW/cm2.Withawideopticalabsorptionwavelengthrangeandhighabsorptionintensity,theCu2O/TNTssamplesareexpectedtobehighlydesirableandpotentialmaterialsforphotocatalyticapplications.

VisiblelightphotocatalyticactivitiesofCu2O/TNTsandTNTs

AsdepictedinFig.S-2,thedarkabsorptionprocesslastsfor60minutesdurationbeforeXearclampwason.ThetypicalabsorptionpeakofAOwasdecreasedwiththeextensionofirradiationtimebyTNTsandCu2O/TNTswithdifferentelectrodepositionchargesundervisiblelightirradiation.ItisobviousfromfigurethatthetypicalabsorptionpeakofAOafterdegradationbyTNTsdecreaseslessrapidlythanthatforCu2O/TNTssamples,indicatingthatCu2O/TNTssamplesexhibitbetterphotocatalyticactivitythanthatofTNTs.

Fig.S-3depictsthecomparisonofadsorptionandphotocatalyticresultofTNTsandCu2O/TNTswithdifferentelectrodepositionchargeundervisiblelightirradiation.Theseresultsshowthat88%oftheAOwasphotocatalyticallydegradedafter2hirradiationusingtheCu2O/TNTswiththechargeof0.5C.TheCu2O/TNTswiththechargeof1.0CexhibithigherphotocatalyticdegradationratethanthatofCu2O/TNTswiththechargeof0.5C.ThephotocatalyticactivityoftheCu2O/TNTswiththechargeof1.5CforAOdegradationismuchlowerthanthatoftwosampleswithonly60%.Forcomparison,theTNTsfunctionasthephotocatalyst,thedegradationoftheAOwasextremelyslow（only20%oftheAOwasdecolorizedafter2hofirradiation）.

UVlightphotocatalyticactivitiesofCu2O/TNTsandTNTs

Fig.S-4depictsaseriesofabsorptionspectraofAOaqueoussolutionafterdegradationbyCu2O/TNTsandTNTsexposedtoXearclampforvarioustimedurationsunderUVandvisiblelightirradiation.Thetypicalabsorptionpeakgraduallydiminishes,suggestingthedegradationofAOassistedbyCu2O/TNTsandTNTs.

Fig.S-5depictsthecomparisonofadsorptionandphotocatalyticresultofTNTsandCu2O/TNTswithdifferentelectrodepositionchargesunderUVandvisiblelightirradiationafter1hXearclampirradiation.TheseresultsclearlydemonstratethatallthreekindsofCu2O/TNTssamplescouldbeeffectivephotocatalystsunderlightirradiation.TheyallexhibitabetterphotocatalyticperformancethanthatofthebareTNTs.TheCu2O/TNTswiththechargeof1.0Cexhibitsthehighestphotocatalyticdecompositionefficiency（theCu2O/TNTswiththechargeof0.5Cislowerand1.5Cistheworst）.

TherepeatedphotocatalyticdegradationofanaqueousAOsolutionundervisiblelightirradiationwasconductedtostudythestabilityoftheCu2O/TiO2compositenanotubearrays.Cu2O/TiO2wasusedforfivesuccessiveAOdegradationexperiments.AsshownintheFig.S-6,thephotocatalyticactivityofCu2O/TiO2isrelativelystable.Althoughsomephotocatalyticactivitylosseswereobservedinfivesuccessiveruns.Theresultsshowthat90%oftheAOwasdegradedafter2hirradiationusingtheCu2O/TNTswiththechargeof1.0Cinthefirstrunand74.6%oftheAOwasdegradedinthefifthrun.

ThephotocatalyticdegradationoftheaqueousAOsolutionledtoasignificantreductionwhentheCu2O/TNTsphotocatalystwaspresent.TheenhancedcatalyticactivityofCu2O/TNTscouldbeattributedtotheheterojunctionconstructionandtheseparationofthephotogeneratedelectronandholeintheheterojunctionstructuretoimprove